Process control apparatus

Abstract

A process control apparatus capable of adjusting control constants of a process control operation which controls a controlled process. The process control apparatus includes an identification signal generator for producing a maximum length sequence signal, an adder for adding this maximum length sequence signal and a control signal and supplying it as an operation signal to a process, an operation circuit for identifying the pulse transfer function of a process response from the process signal and the operation signal and processing the transfer function by Laplace-transforming the step response of the pulse transfer function, and a circuit for processing control constants according to the transfer function.

What is claimed is: 
     
       1. A process control apparatus comprising: set-point signal generating means for generating a set-point signal of an output of said process;   controller means for controlling a process input of said process in accordance with control constants and a control error which is a difference between the set-point signal and said process output;   identification signal generating means for superimposing a persistently exciting identification signal on said process input;   identifying means for identifying a pulse transfer function of said process in accordance with said process input on which the persistently exciting identification signal is superimposed and said process output;   calculating means for calculating an S-transfer function of said process from the pulse transfer function identified by said identifying means; and   control constant generating means for tuning the control constants in said controller means in accordance with a result of model-matching of the S-transfer function calculated by said calculating means with an S-transfer function of a reference process model.   
     
     
       2. A process control apparatus according to claim 1, wherein said identification signal generating means generates a maximum length sequence signal. 
     
     
       3. A process control apparatus according to claim 1, wherein said identifying means is connected to said controller means and comprises a filter of iterative maximum likelihood type to estimate the pulse transfer function according to said process input and said process output. 
     
     
       4. A process control apparatus according to claim 1, wherein said calculating means connects two adjacent step responses at the pulse transfer function obtained by said identifying means with a straight line and Laplace--transforms a function obtained by the connection. 
     
     
       5. A process control apparatus according to claim 1, wherein said calculating means calculates an S-transfer function of a second order process with a dead time, using a step response on said pulse transfer function. 
     
     
       6. A process control apparatus according to claim 1, wherein said calculating means calculates an S-transfer function of said process except that of a sample and hold circuit in the process control apparatus. 
     
     
       7. A process control apparatus according to claim 1, wherein said controller means includes a subtracter for producing a control error between the set-point signal and said process input, and a PID control circuit for controlling said process input according to the control error and control constants, and said control constant generating means produces PID control constants. 
     
     
       8. A process control apparatus according to claim 7, further comprising first operating means connected to said process and transforming said process output to a first signal; a second operating means connected to said identification signal generating means and transforming the persistently exciting signal to a second signal; and a third operating means connected to the subtractor of said controller means and transforming the control error to a third signal. 
     
     
       9. A process control apparatus according to claim 8, wherein said identifying means processes coefficients of autoregressive moving average model of said process responsive to the output signals of said first, second and third operating means. 
     
     
       10. A process control apparatus according to claim 8, wherein said identifying means processes coefficients of moving average model of said process in response to the output signal of said first, second and third operating means. 
     
     
       11. A process control apparatus according to claim 10, wherein said identifying means processes those of coefficients of moving average model of said process which correspond to a finite term, and which further comprises means for determining the amplitude of the persistently exciting signal according to the variance of said process output and further determining a sampling period and an amplitude of the persistently exciting signal in response to a step response of the identified pulse transfer function.